Retrospective and prospective studies will be conducted to more fully define the epidemiology and natural history of viral myopericarditis. Acute and convalescent sera from 381 patients with clinically diagnosed myopericarditis, submitted to this laboratory between 1967 and 1974, and sera from the approximately 70 new cases submitted each year, will be tested by microneutralization for a greater than or equal to four-fold antibody rise and/or specific immunoglobulin (Tg)M antibody to Coxsackieviruses B1 through B5. Immunofluorescence and immunoperoxidase techniques, in conjunction with density gradient serum globulin fractionation, will be investigated as a more rapid and less complex means of detecting and quantitating specific IgM antibody. The relative importance of the different Coxsackievirus B serotypes to the etiology of myopericarditis and the ratio of this entity to all Coxsacievirus B induced disease diagnosed by this laboratory also will be studied. We will seek to establish by contacting referring physicians and patients with and without Coxsackie B associated myopericarditis some of the following data: (a) onset time, (b) clinical course and differences between Coxsackie B and non-Coxsackie myopericarditis (c) descriptive epidemiologic characteristics of the population involved and (d) the course subsequent to the acute epidose especially in regard to the development of chronic cardiac dysfunction. Finally, we will investigate other etiologies likely to be involved in this disease. If the Coxsackie B viruses are responsible for considerable serious cardiac disease, this information would justify efforts to develop a vaccine.